Beat together sugar, eggs and oil in a bowl for 2-3 minutes then.Then sift in the flour, bicarbonate of soda and nutmeg. Stir, then fold in the orange zest, carrots and sultanas until just combined. Pour the mixture into a baking tin lined with greaseproof paper. Bake for about 35-40 minutes at 170°C, until it feels firm and springy to the touch when lightly pressed in the center.While the cake is cooking make the topping by mixing all the ingredients in a bowl until light and fluffy. Cover with cling film and chill for 1-2 hours or until needed.To make the orange glaze whisk all the glaze ingredients together. While the cake is hot, prick with a skewer then spoon the glaze over.When cooled, remove from the tin,spread with the icing and dust with a little cinnamon to serve.